Romanian coal-fired power station meets national pollution directives thanks to deployment of powerful, flexible and scalable DCS solution from Rockwell Automation
Sustainability still remains a massively high priority in the world today, with local, national and international programmes in place to incentivise people, organisations, companies and countries to ‘do their bit’ for the environment.
At an international level, the Paris Climate Agreement is setting ambitious targets, while at a regional level, EU emissions directives are setting an equal amount of pressure on member states to create their own programmes to cut emissions to acceptable levels. with these targets getting tougher to hit as date-related stage gates are reached.
One installation that is feeling the effects of this legislation is a large combined heat and power (CHP) plant in Iași, Romania’s second largest city. Two of the plant’s 420 T/hr steam boilers still operate on pit coal, with a fuel oil back up, and, as is true with many fossil-fuel powered systems, the emissions were less than optimal.
The plant’s operator realised that it needed to better manage and mitigate these emissions – especially the SO2 levels – and took this project as an opportunity to upgrade the entire control infrastructure for the power-generation system. For this project it employed Romanian company Elsaco Electronic SRL – a member of the Rockwell Automation PartnerNetwork™ as a Recognised System Integrator – that specialises in energy, hydro and automation & SCADA, covering a variety of projects not only in Europe but across the world.
Rockwell Automation Recognised System Integrators and Solution Partner companies are proven, trusted and established companies that offer demonstrated knowledge and experience in design, implementation, project management and maintenance of industrial control systems.
According to the end user: “The objective of the heating project in Iași was to create an investment program that would ensure compliance with the environmental obligations set under the Accession Treaty, and with the objectives of the national energy strategies and policies, such as improving energy efficiency, fuel flexibility and heating supply security.”
Environmental directives – especially in terms of emission control of fossil-fuel sources – can be hard targets to hit. A lot of the issues are down to working with an installed base of older equipment that was designed in an era before these targets and directives became common place. In most instances, it is possible to create some improvements in operational efficiencies, such as cleaner burning and tighter fuel control, but in others, where the process itself is not inherently environmentally friendly, you have to deal with the emissions as they are created in order to make them less harmful to the environment.
The CHP plant needed to deploy a new flue gas desulphurisation (FGD) solution in the two boilers’ shared smokestack, which would better manage the SO2 levels, while also undertaking a number of other improvements, such as refurbishing water boilers, electrostatic precipitators, pumps & transfer systems and the installation of low-NOx burners.
In terms of the FGD, the plant had to fulfil stringent performance parameters for SO2 concentration and dust concentration at the flue-gas evacuation outlet, including flue gas desulfurization efficiency and operational availability. The consumption of electricity, the quantity of reagent and the quantity of water used in the process also had to be tightly controlled and managed to remain under certain pre-determined values.
In addition to the scale of the project and the multiple variables, Elsaco, as the system’s designer and integrator, also faced project time constraints, which were compounded by the fact that it had to undertake testing and adjustments in the flue gas loops without damaging any of the existing equipment.
The new FGD plant is used to precipitate acidic compounds, such as SO2, SO3, HCl, HF and dust from the flue gas. It comprises a circulating fluidised bed (CFB) reactor, a fabric filter, a booster fan and multiple auxiliary systems.
In operation, the raw flue gas flows through the circulating fluidised bed, consisting of dry powdered hydrated lime and circulated reaction products. A controlled quantity of pressurised water is sprayed into the reactor to improve the reaction conditions as well as to decrease the raw gas temperature. The cooled and chemically cleaned, particle-laden gas leaves the reactor and enters the fabric filter, which removes any dust. The precipitated solid particles are then collected in a Solids Return Vessel, with most being recycled into the CFB reactor. A small amount is collected in a product silo.
The target of this process was to reduce the SO2 concentration from 2.190 mg/m³ STP dry basis to 50 mg/m³ STP dry basis and to reduce the solids content from 50 mg/Nm³ on 6% dry basis to less than 20 mg/Nm³ on 6% dry basis in the cleaned flue gas.
“For the control of the FDG Plant, the end user accepted our suggestion to deploy the PlantPAx DCS from Rockwell Automation,” explains Bogdan Panzaru, one of Elsaco’s engineers. “PlantPAx DCS offered the performance, flexibility and availability it required and, from our perspective as the system designer, the Rockwell Automation Library of Process Objects available with PlantPAx greatly improved the project’s development time.
“To meet specific customer needs, the DCS needed to offer freely configurable and programmable self-diagnosis components,” he continues, “based on state-of-the-art microprocessors. The customer also needed the flexibility and freedom to further develop the system in order to extract even greater performance in the future.”
In terms of hardware, the PlantPAx DCS solution is supervised by a high-end Rockwell Automation process controller, communicating over a fibre optic EtherNet/IP™ network and managed switches, with a mid-range digital I/O process controller, which oversees and collects data from ancillary equipment. Redundancy is built in at the level of the high-end controller, the servers and the communication system. Operators are able to oversee and control the entire operation from operator workstations (OWS) in a central control room.
PROFIBUS and Modbus communication modules were also used in conjunction with the mid-range controller to communicate with devices that did not directly plug into the EtherNet/IP network. These modules were supplied by ProSoft Technology, another Rockwell Automation PartnerNetwork member, at Global Encompass Product Partner level.
Overall system functions include data acquisition and processing, command and interlock, human-machine interfaces and data storage – for archiving, trends, communication and engineering. High-end HMIs interfaces are used, with a single integrated programming and operating environment, to deliver advance diagnostics and process face plates for pumps, valves, etc.
Thanks to deployment of the industry-proven PlantPAx DCS-controlled FDG – coupled to the refurbishment of the electrostatic precipitators on both boilers – the particulate emissions range is now below 50 mg/Nm3 6% O2. As a result, this element of the plant is now compliant with the particulate-emission norms.
“Elsaco delivered a stable and robust system within a short time period,” “The industry-proven PlantPAx-controlled solution delivers a level of operations that fulfils our requirements in terms of performance and reliability, while allowing us to meet our environmental obligations.”
“We have a great relationship with the Rockwell Automation engineers,” Panzaru concludes. “They gave us really good support, both in the project phase and in the development phase, for which I am really thankful, and I look forward to our future collaborations.”